Pyrolytic conversion of hydrocarbons with recovery of coke



MaY 9, 1951 M. c. FOGLE 2,983,671

RYROLYTIC CONVERSION OE HYOROCARBONS WITH RECOVERY OE COKE Filed May 10, 1951 INVENTOR. /y/a//fjrj/S.

United States Patent O Merald C. Foglie, Oakmont, Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed May 10, 1951, Ser. No. 225,571

IClaims. (Cl. 208-127) This invention relates to the pyrolytic conversion of hydrocarbons with recovery of coke and, more particularly, to a continuous process for converting heavy hydrocarbon oils to coke and valuable light hydrocarbons in the presence of an agitated mass of small, discrete, solid particles.

`In commercial practice the coking of heavy hydrocarbons is generally performed in horizontal batch shell stills or according to the more recently developed delayed coking process. in the latter well-known prior art process, coke is deposited on the inner walls of a coking chamber. To recover the coke it is necessary interrnittently to stop the ow of hydrocarbons tothe coking chamber and cut the coke from the chamber walls hydraulically by means of high pressure water jets Delayed coking thus has the serious disadvantage of being a batchtype process requiring a plurality of expensive coking drums so that flow canbe switched from one to another during the intermittent coke removal periods. Hydraulic or other mechanical methods of coke removal require expensive equipment and constitute another disadvantage of the process.

In attempts to avoid the disadvantages of delayed coking, various processes have been proposed in which the operation is continuous so that only a single coking chamber is required and in which the method of coke removal differs from the hydraulic method. Among the prior art proposals are processes which comprise heating hydrocarbon oil in the presence of a moving solid bed of inert balls so that coke is deposited on the balls and conveying the balls to a suitable coke-removal apparatus, as for example a low pressure chamber, in which coke is split from the balls. The balls must then be conveyed to coke separating means such as screens. Frequently in the proposed processes the conditions are such that the oil is in the liquid phase throughout the treatment so that wet coke is formed which must be separated from liquid hydrocarbons by a diicult filtration. All of these proposals have the serious disadvantage of requiring mechanical conveying means for transporting the inert balls. Processes employing such mechanical conveying means are generally unsatisfactory because of the expense of the equipment required and the problem of mechanical maintenance.

Another objection to these prior art proposals and possibly the most serious obstacle to commercial development of coking processes using a moving bed of inert balls has been in the diiculty of obtaining uniform distribution of the charge oil across the bed of solids without premature coking.

in still another prior art proposed process, coking is accomplished by contacting gaseous hydrocarbons with a hot refractory powder maintained in a fluidized condition. In this proposed process coke is deposited on the powder and is removed from the powder by burning. Therefore, the proposed process does not give coke as a product, which constitutesl one of the advantages of the 2,983,671- Patented May 9, 1961 present invention, and the heat of combustion of the coke in such a process is not ethciently recovered.

The indicated disadvantages in prior art processes are overcome by the present invention and a process is provided in which cokng of heavy hydrocarbon oils can be conducted in a continuous operation using only a single coking chamber, this chamber containing a fluidized bed of inert, discrete, solid particles. The process is conducted in a manner that provides uniform distribution of charge oil throughout the bed of inert solid par# ticles and permits simple and inexpensive recovery of coke.

The invention in general provides a. process which comprises subjecting a hydrocarbon oil to coldng conditions of temperature and pressure while passing said hydrocarbon oil through a suspended bed of discrete, inert, solid particles. The hydrocarbon oil is thereby decomposed and carbon is deposited on the particles. The particles are agitated severely so that deposited coke is removed by the mutual rubbing action of the particles. Coke so removed is carried from the suspended bed of particles with the effluent hydrocarbon vapors and is thereafter separated from the hydrocarbon product.

The drawing shows somewhat diagrammatically and partially in vertical section an apparatus suitable for employment in my coking process. It will be noted that the apparatus illustrated resembles apparatus used in wellaknown uidized catalyst processes such as fluidized catalytic cracking and iluidized' catalytic destructive hydrogenation. My process operates with a mass of inert solid particles maintained in a turbulent state in a manner similar to the mentioned processes and benefits from several of the advantages of fluidized operation.

My process can most conveniently be described by reference to the drawing in which is shown a coking chamber 1 which contains a body of small, discrete, solid particles 2. Coking chamber 1 is provided with a feed inlet 3 and a product outlet 4. A charge of heavy oil such as a reduced crude, is preheated by means of heaters not shown in the drawing to a temperature somewhat below a temperature at which rapid and substantial precoking of the charge would occur and under conditions designed to eliminate insofar as possible such pre-coking, for example, a temperature of 400 to 800 F. The preheated charge, which may be partially vaporized, -is introduced to the reaction vessel 1 through conduit 3 at a relatively high linear velocity which is sutiicient to agitate the mass 2 of particles and maintain them in a turbulent state resembling the turbulence of catalysts in iluidized cracking operations.

The agitated mass of particles in coking chamber 1 is maintained at suitable coking conditions of temperature and pressure such as a temperature of between about 800 and 12.00 F. and preferably 900 to l000 F., and a pressure of from 1 `atmosphere to 200 pounds per square inch gauge. The reaction temperature is maintained by withdrawing a side stream of the particles through conduit 5, heating them in -a suitable heater `6 by direct contact with burning gases and returning them to the coking chamber via line 7 and conduit 3 where they are carried upwardly by the charge stream. lThe temperature in the coking chamber can be controlled by the rate at which the particles are withdrawn for circulation through the heater 6, yas well as by the temperature to which they are heated.

Any suitable coking charge may be used in my process such as crude oil, reduced or topped crude, or heavy petroleum distillates. F. the heavy charge oil may be partially or entirely liquid and it may be necessary to -add steam to the charge to facilitate initial uidization of the bed of pellets and to prevent the formation of a slurry with the pellets.

When preheated to 600 or 800 i At least 60 percent and in some cases as much as 90 or 95 percent of the charge will normally be vaporized with some cracking occurring almost immediately upon contact with the hot pellets. The remainder of the hydrocarbon charge is held `on the surfaces of the pellets obsorbing `additional heat and being converted to a dry coke deposit. Because of the intense agitation, this coke is rubbed olf substantially as rapidly as formed by the mutual rubbing action of the particles. The coke, being lighter than the particles, i.e., `of lower density, is er1- trained in the up-liowing gaseous hydrocarbon stream and is carried out of the coking chamber through outlet 4 'to a suitable separating means such as cylone separator r 8 where it is separated from the gaseous product.

From this cyclone `separator the powdered coke drops downwardly through conduit 9 from which it is recovered as product and the gaseous product is recovered from line 10.

During the process an inert stripping gas such as steam is introduced at different points in the path of solid particles flow to prevent the entrainment from one section of the `system to another of the various reaction components by the solid particles. Several suitable points for introduction of stripping gas are shown in the drawing, for example in the conduit 5 between the coking chamber and the heater, in the conduit 7 leaving the heater, and in conduit 9 by which coke is withdrawn from the cyclone separator.

The linear gas velocity of the coking charge must be sufiicient to maintain an agitated suspended bed of solid particles and suiicient to carry finely divided coke particles out of the coking chamber with the product vapors. Preferably the gas velocity is sufficient to maintain a turbulent fluidized bed of said particles so that the owing vapors alone will sufficiently agitate the solid particles to rub ofiu `deposited coke without the aid of other agitating means. However, my process may be practiced using a mechanical agitator such as a rotating paddle blade to furnish a large measure of the agitation required to remove coke from solid particles. In such case the gas velocity may be sufcient only to blow coke out of the chamber land moderately suspend the bed of particles to lower the resistance to the rotating agitator. In any case the gas velocity should not be so great as to cause solid particles to flow in substantial Yamount overhead with the product vapors and finely divided coke.`

The particles used in my process must be capable of withstanding considerable heat, mechanical shock, and abrasion and should be nonreactive in the process, i.e., under the conditions of the process they should not decompose nor react with any materials contacted during the operation, and preferably they are non-porous and non-catalytic. Thus, they are made from such glass, metal or other refractory materials as Pyrex glass, fused alumina, carborundum, stainless steel, or the like, a common characteristic of each of these substances being that they are of greater density than the petroleum coke formed in the process. However, particles may be used which initially in the process are porous and have catalytic activity, but during operation the particle pores will become clogged with carbon so that catalytic activity will be lost. Since catalytic activity is not a required characteristic of the particles, it would be an unnecessary expense to regenerate carbon-clogged particles and therefore during the main period of use of initially catalytic particles they can be considered as non-catalytic. Thus, in the specilication'and claims when I say that the solid particles are inert I mean that they are nonreactive and normally non-catalytic but I do not exclude particles which have catalytic activity in the initial stages of use but become noncatalytic during the process.

The particles are used in the form of pellets, beads, granules, balls, or the like and are of yany suitable shape such as spherical, cylindrical, cubical or of irregular shape. They may be either solid or hollow. They must not be so small and Ylight as to agglomerate when contacted with a heavy hydrocarbon charge such as reduced crude and they should have sufficient mass so that in rubbing and striking together in the turbulent or iluidized bed they will grind oi any coke which forms on their surface. They must, of course, be of greater density than the petroleum coke formed in the coking process so that separation of the lighter coke from the inert particles will take place readily in the fluidized bed. On the other hand, the particles must be light enough to form a suspended or fluidized bed when blown with the charge oil at a reasonable gas velocity. The size of the particles, which can be expressed in terms of diameter, will depend in part upon the density of the particular material of which the particles are composed. For most materials, particles ranging in diameter from about lyf; inch to M1 inch will be suitable and will be given sufficient agitation at reasonable gas velocities to remove the deposited coke.

The linear gas velocity of the charge which will give the proper agitation to the particles is dependent on the size and density of the particles and can best be determined experimentally by fluidizing a sample of the solid particles to be used. As an example of proper gas velocity with a typical type of solid particles, I can say that the minimum tluidization velocity for 1A; inch fused alumina beads is about 4 feet per second. If a mechanical agitator is employed in the coking chamber, the gas ve` locity may be somewhat lower.

The surface area of the particles determines the throughput of oil which may be handled and since the particles are non-porous` this surface area is the total geometrical surface area of the particles. Normally, to calculate the different process variables the procedure is to decide first the nature of the charge in terms of percent vaporized at reaction conditions and-weight of liquid retained on the solid particles per unit area of solids, the throughput of charge which is desired, and the type of particles which are to be used, i.e. the material of which they are composed and their range of sizes. From this knowledge the required surface area of solid particles can be calculated. Then, knowing the surface area and density of the particles, the weight of particles of the chosen particle size can be calculated with which figure the solids-to-oil ratio can be determined.

I will illustrate the calculations which are necessary for obtaining the solids-to-oil ratio in a typical coking operation according to my invention. In this typical operation, the charge is an 18.5 API Mid-Continent reduced crude. The solid particles are 1A; inch fused alumina balls having a specific gravity of 4.00. Reaction temperature is 900 F. and the pressure is l0 pounds per square inch gauge. Steam is charged with the oil in the amount of 5 pounds per 100 pounds of oil. By assay data -available on this particular crude it is determined that approximately 84.2 percent of the charge is vaporized under these reaction conditions and 15.8 percent of the charge remains unvaporized. This unvaporized charge is retained on the surfaces of the solid particles at 900 F. to the extent of about 0.008 pounds per square foot. I-f the desired charge throughput is 1,000 barrels per day, the amount of liquid which must be retained on the surfaces of the circulating solid particles is 158 barrels per day (1,000 barrels per day 15.8 percent) or 2215 pounds per hour (158 barrels per day 42 gallons per barrel 8.01l pounds per gallon/24 hours per day). Since the liquid is retained on the solid particles in the amount of about 0.008 pound per square foot, the total surface area of the particles which must be provided to accommodate 2215 pounds per hour of liquid is 277,000 square feet per hour (2,215 pounds per hour/0.008 pound per square foot). To supply 277,000 square feet of dry surface area per hour with l; inch beads the hourly volume of solid material (i.e., the volume of beads excluding space between the individual beads) is 481 cubic feet per hour (277,000X1/6 D3/D2=277,000 D/ 6=277,000X 1/96 1/ 6. These beads` have a specific gravity of 4.00 or a density of4,00 grams per cc. Thus, a mass of the beads which contains one cubic foot of solid material weighs 249.6 pounds (4.00 grams per cc. 62.4 pounds per cubic `foot/gram per cc.). Therefore, the weight per hour requirement for beads is 120,000 pounds per hour (481 cubic feetper hour 249.6 pounds per cubic foot). When charging 1,000 barrels per day of 18.5 API reduced crude having a density of 7.856 pounds per gallon, the hourly weight of charge is 13,750 pounds per hour (1,000 barrels per day 42 gallons per barrel 7.856 pounds per gallon/24 hours per day). Therefore, the solids-to-oil ratio is l20,000/l3,750 or 8.7/1.

From the above calculations it is shown that for a throughput of 1,000 barrels per day of 18.5 API Mid- Continent reduced crude using a coking temperature of 900 F. and a pressure of 10 pounds per square inch gauge, the solids requirement is 120,000 pounds per hour of 1/s inch fused alumina balls, or 60 tons per hour. The averageresidence time of the solids in the bed is controlled by the quantity of solids retained in the bed. If the solids are circulated at the rate of 60 tons per hour and the wei-ght of solids maintained in the reactor is 20 tons, the solids will remain in the reactor for an average of `about 20 minutes. 'Ihis time may be shortened or lengthened by adjusting the bed height to give a satisfactory oil contact time for the production of dry coke.

The cyclone-type separator shown in the drawing is one suitable means for separating coke from the gaseous hydrocarbon product. This separator may be placed outside the'coking chamber as shown in the drawing or if desired it may be inside the coking chamber. Any other suitable means for separating gases and solids may also be used. Any coke carried past the separator with the eluent vapors can be recovered in the heavy bottoms of the fractionated product. The heavy bottoms can be further concentrated by suitable thickening equipment and returned to the coldng chamber as a heavy slurry.

`From the foregoing description it can be seen that my process provides a continuous method of coking heavy hydrocarbons using an yapparatus of simple construction, providing a uniform distribution of charge oil across the coking chamber, and permitting a simple and inexpensive method of sep-arating coke from decomposed hydrocarbons. The process produces a petroleum coke which can be used lfor briquetting or for the manufacture of electrodes or lfor other purposes where a high-quality coke is required. My process also yields a valuable hydrocarbon product which contains gasoline and cracking stocks.

Obviously many modications and variations of the invention as hereinbefore set forth may be made without departing `from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

l. The process which comprises subjecting a hydrocarbon oil to coking conditions comprising a temperature of between about 800 and 1200 F. and a pressure of between about 1 atmosphere and 200 p.s.i.g. while passing said oil through a suspended bed of discrete, inert, refractory, solid particles of greater density than petroleum coke, whereby said oil is decomposed and coke is formed on said particles, said particles ranging in diameter from about ye inch to about 1A inch, agitating severely said particles to remove coke deposited thereon by the mutual rubbing action of said particles, passing said oil through said bed at a velocity sufficient to remove substantially all of the coke formed in said process. from said suspended bed of particles together with the hydrocarbon product but insuicient to remove the inert, refractory, solid particles from said bed in substantial amounts, and separating said coke from said hydrocarbon product.

about IAG inch to about 1A. inch, the linear velocity of said oil being sufficient to agitate severely said particles whereby coke deposited thereon is removed by the mutual rubbing action of said particles, and also being suiiicient to blow coke from said iluidized bed but insuicient to blow the inert, refractory, solid particles from said bed in substantial amounts, removing hydrocarbon product from said uidized bed of particles together with entrained coke, said coke being substantially all of the coke formed in said process, and separating said coke from said hydrocarbon product.

3. The process which comprises subjecting a hydrocarbon oil to coking conditions comprising a temperature of between about 800 and l200 F. and a pressure of between about l atmosphere and 200 p.s.i.g. while passing said oil through a iluidized bed of discrete, inert, refractory, solid particles of greater density than petroleum coke, whereby said oil is decomposed and coke is formed on said particles, said particles ranging in diameter from about l@ inch to about 1A inch, the linear velocity of said oil being suicient to agitate severely said particles whereby coke deposited thereon is removed by the mutual rubbing action of said particles and also being sufcient to blow coke from said fluidized bed but insucient to blow the inert, refractory, solid particles from said bed in substantial amounts, maintaining the coking temperature during said process by continually withdrawing a stream of the refractory solid particles from said fluidized bed, passing said stream of particles through a heating means and returning the so heated particles to said uidized bed, removing gaseous product from said fluidized bed of particles together with entrained coke, said coke being substantially all of the coke formed in said process, and separating said coke from said gaseous product.

4. The process which comprises subjecting a hydrocarbon oil to coking conditions comprising a temperature of between about 800 and 1200 F. and a pressure of between about one atmosphere and 200 p.s.i.g. while passing said oil through a mechanically agitated, suspended bed of discrete, inert, refractory, solid particles of greater density than petroleum coke, whereby said oil is decomposed and coke is formed on said particles, said particles ranging in diameter from about 1/15 inch to about 1;/4 inch, the mechanical agitation of said bed being suiicient to remove coke deposited on said particles by the mutual rubbing action of the particles and the linear velocity of said oil being sufcient to blow coke from said suspended bed of particles but insuiicient to blow said inert, refractory, solid particles from said bed in substantial amounts, removing hydrocarbon product and entrained coke from said bed, said coke being substantially all of the coke formed in said process, and separating said coke from said hydrocarbon product.

5. The process' which comprises subjecting a hydrocarbon oil to coking conditions of temperature and pressure while passing said oil through a suspended bed of discrete, inert, refractory, solid particles of greater density than petroleum coke and of diameter greater than about 1/16 inch, whereby said oil is decomposed and coke is formed on said particles, agitating severely said particles to remove coke deposited thereon by the mutual rubbing action of said particles, passing said oil through said bed at a Velocity sufficient to remove substantially all of the coke formed in said process from said suspended bed of particles together with the hydrocarbon product but insulicient to remove the inert, refractory, solid particles from said bed in substantial amounts; and separating Said coke from said hydrocarbon product.

References Cited in the le of this patent UNITED STATES PATENTS 8 Schutte Dec. 21, 1948 Rex et al. Oct. 18, 1949 Roetheli Oct. 31, 1950 Welty Jan. 16, 1951 Odell .Tune Y19, 1951 Friedman July 29, 1952 Schutte Dec. 23, 1952 

1. THE PROCESS WHICH COMPRISES SUBJECTING A HYDROCARBON OIL TO COKING CONDITIONS COMPRISING A TEMPERATURE OF BETWEEN ABOUT 800* AND 1200*F. AND A PRESSURE OF BETWEEN ABOUT 1 ATMOSPHERE AND 200 P.S.I.G. WHILE PASSING SAID OIL THROUGH A SUSPENDED BED OF DISCRETE, INERT, REFRACTORY, SOLID PARTICLES OF GREATER DENSITY THAN PETROLEUM COKE, WHEREBY SAID OIL IS DECOMPOSED AND COKE IS FORMED ON SAID PARTICLES, SAID PARTICLES RANGING IN DIAMETER FROM ABOUT 1/16 INCH TO ABOUT 1/4 INCH, AGITATING SEVERELY SAID PARTICLES TO REMOVE COKE DEPOSITED THEREON BY THE MUTUAL RUBBING ACTION OF SAID PARTICLES, PASSING SAID OIL THROUGH SAID BED AT A VELOCITY SUFFICIENT TO REMOVE SUBSTANTIALLY ALL OF THE COKE FORMED IN SAID PROCESS, FROM SAID SUSPENDED BED OF PARTICLES TOGETHER WITH THE HYDROCARBON PRODUCT BUT INSUFFICIENT TO REMOVE THE INERT, REFRACTORY, SOLID PARTICLES FROM SAID BED IN SUBSTANTIAL AMOUNTS, AND SEPARATING SAID COKE FROM SAID HYDROCARBON PRODUCT. 